Phase Transition and Optical Properties of VO₂ and Al: ZnO/VO₂ Thin Films

Thermochromic Vanadium dioxide (VO₂) has strong potential for smart window applications but its commercial scale usage is limited due to low visible light transmission. To address this issue, aluminum doped zinc oxide (AZO) anti-reflecting layer is integrated with VO₂ layer in the present work. VO₂ single layer and AZO/VO₂ bilayer thin film samples were deposited by sputtering technique on quartz substrate. The single-phase growth of VO₂ and AZO in single layer and bilayer thin film samples is confirmed by X-ray diffraction measurements. Monoclinic M1 phase of VO₂ is detected in VO₂ and AZO/VO₂ thin film samples at room temperature. Monoclinic to rutile structural phase transition (SPT) in these samples is studied by performing temperature-dependent X-ray diffraction measurements. SPT in VO₂ thin film samples is close to 68 °C and SPT temperature appears slightly lower in AZO/VO₂ sample as compared to VO₂ sample. Spectral transmittance measurement at room temperature showed significant improvement in the visible transmittance of AZO bilayer film than that of single layer VO₂ thin film. These results demonstrate the possibility of integration of anti-reflecting layers such as AZO with VO₂ layer for better visible transmittances suitable for large-scale smart window applications.